1. Field of the Invention
The present invention relates to a universal fixture and, more particularly, is directed to an automatically driven universal fixture used to position or measure a component.
2. Background Information
Most modem machine shops that perform large-scale production operations are typically equipped with one or more universal fixtures. In the aerospace industry, for example, universal fixtures are used to support panels having specific contours. Such a fixture may consist of a matrix of adjustable nail-like supports protruding from a surface. Other forms of universal fixtures, such as disclosed in a patent to Speller, Sr., et al. (U.S. Pat. No. 4,821,408), are directed to a universal fixture for holding an assembly to be operated on by a numerically controlled ("NC") machining apparatus. The assembly may be a strip-type assembly, such as a wing webbing. Yet another form of universal fixture is a contour checking fixture 310, as shown in FIG. 1, which is used to measure the contour of a tolerance critical component 320, such as a stringer of an airplane wing.
In the contour checking fixture 310 of FIG. 1, the component 320 to be measured is positioned between a series of stations 322a-322g and a contour template 324, both of which are mounted on a floor check fixture 325. The actual contour of the component 320 is compared with the contour of the contour template 324, which represents the required contour and dimensions of the component 320.
The contour template 324 includes a series of thin aluminum sheets 326a-326d, each of which is carefully machined by an NC machining apparatus. Each of the sheets 326a-326d of the contour template 324 has one surface that precisely matches the required contour of the component as specified by engineering drawings. Each of the sheets 326a-326d is separately fastened to the floor check fixture 325.
The stations 322a-322g are positioned parallel to one another on the floor check fixture 325. Further, each of the stations 322a-322g includes respective plastic braces 332a-332g positioned perpendicular to the contour template 324 which press against the component 320 to push the component 320 toward the contour template 324. Each of the braces 332a-332g is moved into position and held there by respective pneumatically powered pistons 334a-334g movable within a respective pneumatic housing 336a-336g and powered by air supplied via pneumatic hoses 338. The braces 332a-332g are slidably coupled to their respective stands 335a-335g using at least two loose-fitting nut and bolt assemblies 331 (shown on brace 332a). When pushed by the pistons 334a-334g, the respective braces 332a-332g slide along tracks (not shown) within the stands 335a-335g.
When the component 320 is measured, any former contour template is removed piece by piece and stored. Then, the required contour template 324 is carefully fastened onto the floor check fixture 325. Next, each of the stations 322a-322g is slid along tracks 342a, 342b, etc., within the floor check fixture 325 assisted by rollers 44 until each of the stations 322a-322g has been positioned within an inch or so of the width of the component 320. The stations 322a-322g are then locked into position with a locking mechanism (not shown). Next, the component 320 is placed between the contour templates 324 and the braces 332 of each of the stations 322a-322g. Then, air is supplied by an air source 351 via the air hoses 338 to the pneumatic housings 336a-336g, causing the pneumatic rods 334a-334g to push a respective one of the plastic braces 332a-332g against the component 320 with a force of approximately 5 pounds. Once the component 320 is securely braced against the contour template 324, a feeler gauge is used by an inspector to take careful measurements between the actual component 320 and the contour template 324 to measure the component's deviation from the template. The measured deviations are used to determine whether the component is within acceptable tolerances. If the component 320 is within tolerance, it is removed and replaced by a similar component and the process is repeated. When a new component is measured, the contour template 324 is removed and replaced by another template corresponding to the required contour of the new component.
However, the process of replacing the contour template 324 can take a group of workers up to an hour. Thus, if seven different components each having different contours are measured within a day, seven hours of the day are used just to set up and break down the fixture for the measurements. This set-up and break-down process is not only time-consuming, but also extremely costly since skilled labor must perform this task. Also, it is easy to introduce error into the template 324 during its installation. Further, the contour template 324 can be bulky and heavy, and is potentially dangerous to swap out. Unfortunately, efforts to make the contour template 324 less bulky, i.e. putting holes 328 within the contour template 324, and making the aluminum very thin, have the drawback of making the contour template 324 weak and flimsy and potentially bendable during the measurement process. Once the contour template 324 has been damaged, a brand-new contour template must be built with an NC machining device at great cost. Finally, when not in use, the contour templates must be stored, requiring the use of expensive floor space within the factory.
Consequently, in the art of universal fixtures, especially where the fixtures are used to measure contours of components, there is a need for a device that will automatically set up a fixture for a component quickly, inexpensively, and without the need of a fixed template.